If there is a best thing in the world, it might as well be creating. Biology dictates that we (pro)create and pass on our genes. As once one wise man said:

Chicken is an egg's way of making another egg

But I think biology does not stop there. We feel most in the moment hence peaceful when we are creating things.

what is the best thing to create ?

It might be children, as most parents feel that way.

but Lets first divide things into hardware and software, moreover soft and hard, myth and physical.

Software might be the best thing as its reach has prooved it to be quite majestic. It can reach millions of people, impacting their lives just by a click of a button.

Food might be the best thing as it cherishes one of our basic needs- To survive.

But we are not mere single celled organisms. We are intellectual beings.

Ideas translate both space and time. Media reaches billions of people. Ideas make people do what is worst and what is best.

Ideas guide us through our lives.

But what form of idea then?

Stories. Story telling is how we survived and banded together. We are all stories.

To Quote tyrion lannister

“What unites people?” Tyrion asked. “Armies? Gold? Flags?” No. It’s stories, he said. “There's nothing in the world more powerful than a good story. Nothing can stop it. No enemy can defeat it."

So I beleive creating good ideas and good stories is the best of things.